NullPointException in Hive UDAF

NullPointException in Hive UDAF

all
I Write a hive UDAF, when add it to hive. It throws NullPointException
The code and entire task logs is pasted on github gist -->
https://gist.github.com/hellojinjie/6750572
Any idea why it throws NullPointException?
Or why it says :
stderr logs java.lang.reflect.InvocationTargetException Continuing ...
java.lang.IllegalArgumentException: Unbound variable:
GenericUDAFCdnBytesLoaded$GenericUDAFCdnBytesLoadedEvaluator0 Continuing
...
I am a beginner of hive..hehe